1. Field of the Invention
The present invention relates to a display device and a method of fabricating a display device, and more particularly, to a liquid crystal display device having patterned spacers and a method of fabricating a liquid crystal display device having patterned spacers.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device makes use of optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite orientational alignment that results from their long thin shape. The orientation of the liquid crystal molecules can be controlled by application of an electric field to the liquid crystal molecules. Accordingly, as an intensity of the applied electric field changes, the orientation of the liquid crystal molecules also changes. Since incident light through a liquid crystal material is refracted due to an orientation of the liquid crystal molecules resulting from the optical anisotropy of the aligned liquid crystal molecules, an intensity of the incident light can be controlled and images can be displayed.
Among the various types of LCD devices commonly used, active matrix LCD (AM-LCD) devices, in which thin film transistors (TFTs) and pixel electrodes connected to the TFTs are disposed in a matrix configuration, have been developed because of their high resolution and superior display of moving images.
The LCD device includes upper and lower substrates, and a liquid crystal layer interposed therebetween. The upper substrate and lower substrate are commonly referred to as a color filter substrate and an array substrate, respectively. A common electrode and color filter layers are formed on the upper substrate through processes for fabricating a color filter substrate. Similarly, TFTs and pixel electrodes are formed on the lower substrate through processes for fabricating an array substrate.
After the fabricating processes, the LCD device undergoes a liquid crystal cell process where a liquid crystal layer is formed between the upper and lower substrates. The liquid crystal cell process may be divided into a process of forming an alignment layer to align the liquid crystal molecules, a process of forming a cell gap, a process of attaching the color filter and array substrates together, a process of cutting the attached color filter and array substrates into cells, and a process of injecting the liquid crystal molecules. Accordingly, a liquid crystal display panel is fabricating using the liquid crystal cell process.
FIG. 1 is a cross sectional view of a liquid crystal display device according to the related art. In FIG. 1, upper and lower substrates 10 and 30 are spaced apart from each other, and a liquid crystal-layer 50 is interposed therebetween. A gate electrode 32 is formed on an inner surface of the lower substrate 30, and a gate insulating layer 34 is formed on the gate electrode 32. Then, a semiconductor layer 36, which includes an active layer 36a and an ohmic contact layer 36b, is formed on the gate insulating layer 34 over the gate electrode 32. Next, source and drain electrodes 38 and 40 are formed on the semiconductor layer 36, wherein a portion of the active layer 36a is exposed between the source and drain electrodes 38 and 40 to form a channel region “ch.” Accordingly, the gate electrode 32, the semiconductor layer 36, and the source and drain electrodes 38 and 40 constitute a thin film transistor (TFT) “T.”
Although not shown in FIG. 1, a gate line connected to the gate electrode 32 is formed along a first direction, and a data line connected to the source electrode 38 is formed along to the second direction perpendicular to the first direction, wherein a plurality of pixel regions “T” are defined by crossings of the gate and data lines. In addition, a passivation layer 42 having a drain contact hole 44 is formed on the TFT “T,” and a pixel electrode 48 is formed on the passivation layer 42 within the pixel region “P,” wherein the pixel electrode 48 is connected to the drain electrode 40 through the drain contact hole 44.
In FIG. 1, a color filter layer 14 corresponding to the pixel electrode 48 is formed on an inner surface of the upper substrate 10 in order to filter light having specific wavelengths. A black matrix 12 is formed in a boundary region of the color filter layer 14 in order to prevent light leakage and to shield incident light from influencing the TFT “T,” and a common electrode 16 is formed on the color filter layer 14 and the black matrix 12. In addition, a liquid crystal layer 50 is formed between the pixel electrode 48 and the common electrode 16, wherein voltage is supplied to the liquid crystal layer 50 through the pixel electrode 48 and the common electrode 16.
In addition, a seal pattern 52 is formed in a periphery of the upper and lower substrates 10 and 30 to prevent leakage of the liquid crystal layer 50. The seal pattern also maintains a uniform cell gap distance between the upper and lower substrates 10 and 30. Ball spacers are 54 disposed between the pixel electrode 48 and the common electrode 16 to maintain the uniform cell gap along with the seal pattern 52. Although not shown, upper and lower alignment layers may be formed on the common electrode 16 and the pixel electrode 48, respectively, to align the liquid crystal molecules.
Since the liquid crystal layer 50 is driven by a vertical electric field generated between the common electrode 16 and the pixel electrode 48, the LCD device has superior transmittance and a high aperture ratio. However, since the vertical electric field makes the substrate and aligns a long axis of the liquid crystal molecule perpendicular to the upper and lower substrates 10 and 30, the LCD device has a narrow viewing angle.
FIG. 2 is a cross sectional view of an In-Plane Switching-mode liquid crystal display device according to the related art. In FIG. 2, upper and lower substrates 60 and 70 are spaced apart from each other, and a liquid crystal layer 80 is interposed therebetween. Since both a common electrode 62 and a pixel electrode 64 are formed on an inner surface of the lower substrate 70, the liquid crystal layer 80 is driven by a horizontal electric field generated between the common electrode 62 and the pixel electrode 64. Accordingly, a long axis of liquid crystal molecules of the liquid crystal layer 80 is aligned parallel to the lower substrate 70. For example, since the liquid crystal molecules are arranged by a horizontal electric field, displayed images may be viewed at a viewing angle between about 80° and about 85°. Thus, the IPS-mode LCD device has a wider viewing angle than the LCD device using a vertical electric field to align the liquid crystal molecules.
In the IPS-mode LCD device, since both of the common electrode 62 and the pixel electrode 64 are formed on the lower substrate 70, an additional electrode on the upper substrate 60 may be omitted. Accordingly, a top layer may be formed over the inner surface of the upper substrate 60 to provide a high step difference. Thus, an overcoat layer (not shown) may be formed to improve planarization properties of the color filter substrate and patterned spacers or column spacers may be formed on the overcoat layer. The patterned spacers are formed using a photoresist (PR) of a photosensitive organic material using photolithographic processes, which include exposure and development steps.
In FIG. 1, the ball spacer 54 may be made of an elastic material deformable to applied external pressure, such as glass fiber or an organic material. However, since the ball spacers 54 are randomly distributed between the upper and lower substrates 10 and 30, an inferior alignment layer may be formed due to movement of the ball spacers 54. In addition, light leakage may occur within regions adjacent to the ball spacers 54 due to an adsorption force between the liquid crystal molecules adjacent to the ball spacers 54, and a uniform cell gap may not be obtained in a large-sized LCD device. Furthermore, since the ball spacers 54 are elastic and do not remain at a fixed position, a severe ripple phenomenon may occur when the LCD device is touched. Thus, superior display quality can not be obtained in the LCD device using the ball spacers 54 to maintain a uniform cell gap.
On the other hand, a uniform cell gap may be easily obtained using the patterned spacers since they are formed in a non-pixel region, thereby preventing light leakage and improving contrast ratio. In addition, the patterned spacers may be applied to an LCD device requiring a small cell gap due to precise control of the cell gap. Furthermore, since the patterned spacers are fixed, they may be easily applied to large-sized LCD devices and the ripple phenomenon may be prevented when the LCD device is touched. Since the patterned spacers may be formed directly on the overcoat layer in an IPS-mode LCD device, reliability of the patterned spacers is improved.
FIGS. 3A to 3D are cross sectional views of a process for fabricating a color filter substrate of a liquid crystal display device according to the related art. In FIG. 3A, a black matrix 114 having an open portion 112 is formed on a substrate 110, and a color filter layer 116, which includes red, green, and blue sub-color filters 116a, 116b, and 116c, is formed on the black matrix 114. The color filter layer 116 may be formed using photolithographic processes that include a negative-type color pigment, wherein a portion of the negative-type color pigment is exposed through a mask and remains as a pattern after a development step. Although not shown, the black matrix 114 is disposed in a periphery of each sub-color filter as a single body.
In FIG. 3B, an overcoat layer 117, such as an organic material having excellent planarization properties, is formed on the color filter layer 116.
In FIG. 3C, a negative type photoresist (PR) layer 118 is formed on the overcoat layer 117, and a mask 120 is disposed over the negative-type PR layer 118. Then, the negative PR layer 118 is exposed through the mask 120 that includes a transmissive portion 120a corresponding to the black matrix 114 and a shielding portion 120b. Accordingly, a portion of the negative-type PR layer 118 is exposed through the transmissive portion 120a and remains as a pattern after a subsequent development step.
In FIG. 3D, a patterned spacer 122 is formed through a development step of the exposed negative-type PR layer 118. After developing the exposed negative-type PR layer 118, a curing step may be performed to stabilize a structure of the patterned spacer 122. Although not shown, the patterned spacer 122 overlapping the black matrix 114 corresponds to a metal line on an array substrate.
According to the related art, the patterned spacers are obtained using photolithographic processes after forming an overcoat layer in order to ensure uniformity. Then, a negative-type PR layer is formed on the overcoat layer using a coating step, and the negative-type PR-layer is treated using an exposure step, a development step, and a curing step in order to obtain the patterned spacers. Thus, the processes used to form the patterned spacers are complex, and since a negative-type PR is used, the patterned spacers may not be stable.